1. Field
The disclosure relates to a structure of a battery pack including a battery module containing a plurality of cylindrical batteries.
2. Description of Related Art
Battery packs configured by housing battery sets including a number of batteries connected in series or in parallel in casings are used in electric-motor vehicles or the like. Such battery packs cause problems, such as decrease in output thereof and decrease in recharging capacity, if the temperature thereof becomes lower. To cope with this, there has been a proposal to provide a battery pack with a heater so as to heat each battery by this heater if the temperature thereof is low.
For example, Japanese Patent No. 5392407 discloses a technique regarding a battery back including: a plurality of cylindrical batteries; and a metallic battery holder that holds the plurality of cylindrical batteries, wherein a heater is directly disposed to a side surface of the battery holder so as to heat the cylindrical batteries through the battery holder.
Japanese Patent Application Publication No. 2012-243535 discloses a technique regarding a battery pack including: a plurality of cylindrical batteries; and a battery holder partitioned into separated battery housing spaces in each of which each cylindrical battery can be housed, wherein a heating element is disposed with a heating surface thereof in contact with part of an outer circumferential surface of each cylindrical battery so as to directly heat the part of each cylindrical battery by the heating element.
Japanese Patent Application Publication No. 2008-053149 discloses a battery pack including: stacked batteries formed by stacking a plurality of square batteries; a casing that houses the stacked batteries, and has a separator providing separation from the stacked batteries; and a heater disposed adjacent to an outer surface of the separator, wherein the battery pack is configured to heat each square battery through air present between the separator and the batteries.
In a battery set including a plurality of batteries connected in series or in parallel, a difference in temperature among the batteries might cause non uniform charge-discharge behavior among the batteries. Therefore, particular batteries experience significant decrease in residual capacity, which might cause progress of deterioration to the particular batteries. Hence, it is important in a battery set configured by the plurality of batteries to maintain a uniform temperature among the batteries.
Unfortunately, as in the case of the technique described in JP 5392407 B, if the heater is directly disposed to the battery holder, the portion of the battery holder in contact with the heater is locally heated, thus causing a difference in temperature among the batteries heated through the battery holder, which results in variation in temperature among the heated batteries. As in the case of the technique described in JP 2012-243535 A, in a method of bringing a heating surface of each heating element to be in contact with part of the outer circumference of each cylindrical battery, there occurs difference in temperature between part of each battery in contact with the heating surface and part of this battery out of contact with the heating surface, thus causing difference in inner temperature of the same battery, which might result in variation in temperature among the heated batteries. In addition, in the technique described in JP 2008-053149 A, since a gap cannot be provided below each mounting portion that supports the stacked batteries in the casing, this mounting portion cannot be heated by the heater, which might cause variation in temperature among the heated stacked batteries. As aforementioned, in the techniques described in JP 5392407 B, JP 2012-243535 A, and JP 2008-053149 A, the temperatures of the heated batteries in the battery packs may vary.